1. Field of the Invention
The present invention relates to rotating machinery and, more particularly, to a locking mechanism for selectively locking the components of a rotary machine.
2. Description of the Prior Art
A requirement exists in various types of rotating power machinery, particularly with regard to certain types of hand-held power tools, for selectively locking the power transmitting components of the machine to permit convenient removal and replacement of machine-related parts. For example, in portable electric drills, it is desirable to lock the output spindle to effect convenient removal and replacement of the tool-gripping chuck, and, in hand-held grinder/polishers and similar surface-treating machines, it is desirable to selectively lock the output spindle so that the surface-treating disk (for example, a polishing pad, a sanding disk, or grinding disk) can be readily replaced.
Prior locking devices and mechanisms have typically included a locking pin mounted in the tool housing for limited-stroke movement between a retracted, non-locking position and an extended, locking position. The lock pin is typically urged toward and to its retracted position by a spring and is designed to be manually pushed or depressed so that the inward end of the locking pin enters and engages a pin-receiving bore formed in one of the power transmitting components of the machine. Typically, the pin is mounted in the tool housing adjacent to and for insertion into a bore formed in a shaft, spindle, or gear. These prior locking mechanisms have been generally satisfactory, although they have certain drawbacks. For example, many power tools, such as high-speed pneumatic or electric grinder/polishers, require a coast- or run-down time after supply power is removed so that the moving components will come to a complete stop. Oftentimes, the tool operator will inadvertently depress the locking pin before the rotating power transmitting components have come to a complete stop. The locking pin can enter the pin-receiving bore to cause an unintentionally abrupt locking of the machine. The abrupt lock pin engagement, while the power transmitting components are still in motion, can cause a shock-loading effect that can damage spindles, gears, and bearings. Additionally, as occasionally happens, the lock pin can shear or deform to jam the machine.
In recognition of the above-described problems, safety mechanisms have been developed to prevent unintentional lock pin engagement while the rotary components of a machine are in motion. For example, U.S. Pat. No. 3,872,951, assigned in common herewith, discloses an open loop of spring wire attached to a rotatable machine spindle with the trailing end of the wire loop partially bridging the mouth of a lock pin-receiving bore. The trailing end of the spring wire prevents the lock pin from entering the bore unless a specific sequence of manual steps are performed, which sequence of steps can be performed only after the rotating components of the machine have come to a complete halt. While this safe-locking mechanism fully meets its goals, a cost increment is incurred because of the additional number of piece-parts and additional machining steps required to accommodate the safe-lock mechanism.
In another design, a disk-like member is keyed or splined to the tool output shaft adjacent to the output gear and includes a diametric slot formed on one face for receiving the extended end of a locking pin. Camming surfaces are provided on the axial face between the slots so that the extended end of a locking pin will engage the camming surfaces and be urged toward the retracted position of the tool when the tool components are in motion. As in the case of the spring wire safe-lock mentioned above, the requirement for an additional piece-part in this latter safe-lock mechanism adds a cost increment to the tool and, additionally, limits the lower limit of the tool envelope or "compactness" attainable because the tool housing must now accommodate an additional piece-part mounted on its output shaft.